Toxoplasma gondii

MICROBIOLOGY

Protozoan parasite, oocysts shed by cats (definitive hosts).

Oocysts sporulate and become infectious after 1-5 days, are resistant to freezing, and survive > 1 yr in moist environments, e.g., soil. Oocysts transform into tachyzoites, localize in muscle and neural tissue, then develop into tissue bradyzoites.

Transmitted by:

Ingestion of sporulated oocysts via contamination of litter box, sandbox or garden as well as drinking water, fruits and vegetables, or raw seafood. [9]

Ocular disease: in infants, children, or adults with congenital retinochoroiditis; during pregnancy; and in acute or reactivated infection in immunocompromised host.

Most common cause of posterior uveitis. dx by ophthalmologic exam.

Retinochoroiditis, intensely white lesions in clusters, with vitreous inflammation, satellite lesions, retinochoroidal scar, retina vasculitis, and granulomatous anterior chamber inflammation in a third of patients. [2] May cause visual field loss if located near the optic disc.

Self-limited disease in immunocompetent; lesions in acute infection most often unilateral and spare the macula. Those with late sequelae of congential infection have bilateral disease, retinal scars and macular involvement.

Active retinochoroiditis, esp. in immunocompromised host, may present as reduced visual acuity due to intense vitritis, macular traction, or detachment. Treatment aim to control damage to retina and optic disc and decrease tachyzoite load. [3]

Comment: Review of ocular toxoplasmosis treatment finds TMP-SMX is preferred first-line therapy with intravitreous clindamycin plus dexamethasone as an alternative in those who are unresponsive or cannot tolerate oral tx or during pregnancy, TMP-SMX is effective secondary preventive therapy, and corticosteroids without antiparasitics should be avoided as this can lead to fulminant necrotizing retinochoroiditis.

Comment: Serological screening remains the main tool for prevention of congenital toxoplasmosis along with educating mothers to be about potential risk factors. This paper reviews many of the complex diagnostic and treatment decisions of this infection during pregnancy.

Panel on Antiretroviral Guidelines for Adults and Adolescents. Guidelines for Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents. Department of Health and Human Services. Available at: http://aidsinfo.nih.gov…. Accessed 3/23/15.

Comment: In era before ART, 33% of those seropositive for T. gondii w/AIDS not on OI prophylaxis developed toxoplasmic encephalitis in 12 month period. Immune reconsistution on ART, chemoprophylaxis if CD4 < 100, and exposure prevention are priorities. TMP-SMX DS 1 tab po qd is preferred, recommended alternative is dapsone-pyrimethamine plus leucovorin. Discontinuation of primary prophylaxis in those with CD4 >200 for >3mos.

References

Comment: Cross-sectional study correlated serum antibody to 11-kDa sporozoite protein in 59 of 76 (78%) acutely infected mothers who transmitted T. gondii to their fetuses in utero to known risk factors, i.e., exposure to cats, oocyst-contaminated soil, and meat not cooked to well-done. Detection of anti-sporozoite antibodies identified oocysts as infection source rather than bradyzoites in tissue cysts. Transmission risks were identified in 49%, suggesting that undetected contamination of food and water by oocysts may be frequent and unrecognized source of infection. Furthermore, US does not employ gestational serologic screening program, which given the lack of reliable risk factors, would have the greatest likelihood of preventing fetal disease.Rating: Important

Comment: Characterization of ’Amazonian toxoplasmosis’ manifest as acute, disseminated toxoplasmosis with pneumonia in French Guiana included 11 patients (9 men, 8 permanent forest-dwellers, 8 with dietary risk factors, i.e., ingestion of raw game meat, carpaccio) treated with sulfadiazine and pyrimethamine, 2 switched from sulfadiazine to clindamycin. Authors suggest that T. gondii strains found in Amazon basin are more aggressive and result in severe pulmonary disesase more often than strains isolated in Europe and North America.Rating: Important

Comment: Global seroprevalence of T. gondii in women of child-bearing age and during pregnancy based on published reports including at least 100 indivuduals of general population, excluded at-risk populations, i.e., HIV+, immunocompromised, and slaughterhouse workers. Highest rates (>60%) in Brazil and Madagascar, 40-60% seroprevalence in Cuba, Columbia, southern Mexico. Authors note that high seroprevalence may translate to protection from primary infection during pregnancy, and conversely, in areas of low prevalence, an increased risk of primary infection, abortion, and congenital toxoplasmosis.Rating: Important

Comment: In vitro drug release kinetics described for intracular biodegradable polymer implant suggest that in vivo long-term controlled release of clindamycin could be used to treat retinochoroiditis and avoid adverse effects of oral therapy and repeated intravitral injections.Rating: Important